Production of ethylene oxide

ABSTRACT

Process for the recovery of ethylene oxide (EO) from fat absorbent (FA) which comprises providing a feed of elevated temperature FA to an EO Stripper, providing a stripping gas feed and contacting the stripping gas feed at elevated temperature with the elevated temperature FA feed, obtaining stripped lean absorbent (LA) and an EO-containing gas, and providing one or more external process stream feeds to the EO Stripper at a location above the elevated temperature FA feed and at a lower temperature with respect to the elevated temperature FA feed thereby concentrating EO in the EO-containing gas. The process can also include one or more impurity removal stages in the form of one or more side draws from the EO Stripper or an EO Stripper Concentrator. The invention also includes an apparatus for performing the process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. application Ser. No. 11/382,624, filed May10, 2006 now U.S. Pat. No. 7,598,406, now allowed, which application ishereby incorporated by reference.

This application claims the benefit of European Patent Application No.05252851.0, filed May 10, 2005 which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to the production of ethylene oxide, mostsuitably within an integrated ethylene oxide/ethylene glycols process.

BACKGROUND OF THE INVENTION

Ethylene oxide (EO) is an intermediate product for making a wide varietyof derivatives, the most important derivatives in terms of volume beingthe ethylene glycols (EG). Other derivatives include ethanolamines,glycol ethers, detergent ethoxylates, polyols and others. EG is producedby the reaction of EO with water, producing mono ethylene glycol (MEG)as the main product with di ethylene glycol (DEG) and tri ethyleneglycol (TEG) as by-products.

MEG is mainly used for the manufacture of polyester fibres, polyethyleneterephthalate (PET) and, to a lesser extent, in the cooling systems ofmotor vehicles where it serves as antifreeze. DEG is also used in thefibre industry and as tobacco humectant. DEG and TEG are both used forgas drying. TEG is also used in the manufacture of cellophane for foodpackaging.

The production of ethylene oxide is described in Kirk-OthmerEncyclopedia of Chemical Technology, 3^(rd) edition, Volume 9, 1980,pages 443 to 447. The production of ethylene glycols is described inUllmann's Encyclopedia of Industrial Chemistry, 5^(th) edition, Volume A10, 1987, pages 104 and 105.

EO is often produced in a combined EO/EG process, which has theadvantages that the EO process intrinsically has some glycols formationthat requires work up, and that the combined process provides veryefficient heat integration. The integrated process is usually split upinto four sections: EO reaction and recovery; Light ends (LE) removaland EO purification; Glycols reaction and dewatering; and Glycolspurification.

The present invention has application in the first section, EO reactionand recovery, which comprises an EO reactor in which EO is produced bycatalytic gas phase oxidation of ethylene with a molecularoxygen-containing gas, a recycle loop for recycling unconverted reagentsand removing products (EO, water and CO₂) and supplying fresh feeds, anEO Absorber and Stripper for EO recovery from absorbent by absorption inwater and concentration, and a CO₂ removal section.

The general process conditions that apply for the EO recovery section inthe prior art and also for the present invention are suitably anelevated temperature pressure. Herein an elevated temperature indicatesa temperature above ambient. Similarly elevated pressure indicates apressure in excess of atmospheric pressure. The recovery section mayhowever operate at a temperature in the range of from ambient, forexample 20° C., to 150° C., and a pressure in the range of from 100 to1,000 kPa, for example from 200 to 400 kPa. An EO Stripper column willoperate with a temperature and pressure differential from top to bottom.

In a prior art system shown in FIG. 1, loopgas (not shown) from an EOReactor enters the bottom part of the EO Absorber (1). The gas travelsupwards and is washed with Lean Absorbent (LA) which is substantiallyEO-free. The almost EO-free top gas (not shown) is recycled back to theEO reactor system. In the EO absorber the EO is absorbed in the LA andexits as Fat Absorbent (FA) (11). FA (12) from the Residual Gas Absorber(RA) (2) is added to this stream. Cold FA (11, 12) flows through LA/FAheat exchanger (3) and is heated up.

The heated FA (13) enters the top of the EO Stripper (4). An EO/watermix leaves the EO Stripper over the top (14). In the bottom part of theEO Stripper heat is supplied by live steam or by means of a reboiler.Here also some LA is removed as glycol bleed and glycol removed from theLA. The water balance of the system is adjusted with a live steam orcondensate stream (15) to the EO Stripper (4). Hot LA leaves the EOStripper (4) over the bottom (16). In the LA/FA heat exchangers (3) thehot LA is cooled down. To get the correct temperature for absorption theLA is further cooled in other heat exchangers (5). The LA is thenavailable for re-use in the EO Absorber (1) via line 17 and the RA (2)via line 18.

Analysis of the recovery section in one plant showed that in the EOStripper approximately 30 MW of heat is used, whereas for theevaporation of EO only 7 MW is required. The explanation that much moreheat is required in that plant is that about 17.5 MW is used to heat upLA and 7 MW is used to evaporate water out of the top of the EOStripper. Moreover some impurities are present in the EO Stripperoverhead which negatively affect the downstream EG process.

Accordingly there is a need to conserve energy which is currentlyconsumed in evaporating a significant amount of water and removing it asvapour, and which appears to be unnecessary for separation purposes.Moreover there is a need to remove impurities originating in the EOprocess.

U.S. Pat. No. 4,875,909 (NSKK) discloses a method for the recovery of EOfrom such a process in order to reduce the heating energy of the EOStripper. In this publication a prior art line up is disclosed in whicha reduction of water in the EO Stripper overhead is achieved by creatinga rectification in the EO Stripper with reflux of (partly) condensed topproduct. This refluxed material has to be evaporated again, costingenergy. In this line-up, hot FA is fed to the upper part of an EOStripper and (partly) condensed EO Stripper overhead vapor is returnedto the top of the EO Stripper.

U.S. Pat. No. 4,875,909 discloses further line-ups to recover more heatfrom the top vapour of the EO Stripper and to recover heat from the EOStripper bottoms using the following methods:

-   -   flash the bottom stream and apply vapour recompression of the        flashed steam and use that steam in the EO Stripper    -   use the bottom stream further as a heat medium in a refrigerator        system    -   use the bottom stream (after being used in other heat recovery        possibilities) as a heat source in the EO Refiner located in the        EO Stripper bottom stream, or in the LE Column.

In this publication the third characteristic of the apparatus and methodrelates to the heat content of the diffusate from the top of the EOStripper. Lower heat content is achieved by lower water concentrationsof the EO Stripper tops. This again is achieved by a reflux with partlycondensed overhead vapors of the EO Stripper (in a reboiler of the LEColumn). With less water going over the top, also less water has to beevaporated.

To make use of the heat content of the EO Stripper tops of thispublication, even under conditions where it contains much less water,the pressure can be increased, in that way increasing the dew point. Theheat content can then be used as a heat source for the EO Refiner.

SUMMARY OF THE INVENTION

We have now surprisingly found that by providing an additional FA feed,which is not heated, in the EO Stripper, an EO Stripper Concentratorstage is provided having particular heat duty advantages in terms ofproducing a concentrated top stream having reduced water content.Further advantageous embodiments have led to the further downstreamadvantage of combining the EO Stripper and the Residual Gas Absorber(RA) in a single unit.

Accordingly in a first aspect of the invention there is provided aprocess for the recovery of ethylene oxide (EO) from fat absorbent (FA)which comprises providing a feed of elevated temperature FA to an EOStripper, providing a stripping gas feed and contacting the strippinggas fee at elevated temperature with the elevated temperature FA feed,obtaining stripped lean absorbent (LA) and an EO-containing gas, andproviding one or more external process stream feeds to the EO Stripperat a location above the elevated temperature FA feed and at a lowertemperature with respect to the elevated temperature FA feed therebyconcentrating EO in the EO-containing gas.

The present invention also provides apparatus to perform the process ofthe invention which comprises an apparatus for recovery of ethyleneoxide (EO) from fat absorbent (FA), which comprises an EO Stripperhaving an inlet for FA, an inlet for stripping gas, outlets for strippedlean absorbent (LA) and EO, and one or more inlets located above the FAinlet for one or more external process streams.

Accordingly there is provided an apparatus for recovery of EO from FA,comprising an EO Stripper having an inlet for elevated temperature FA,an inlet for stripping gas for contacting at elevated temperature withthe elevated temperature FA, and outlets for stripped LA and EO,characterised in that the EO Stripper is an EO Stripper Concentrator forconcentrating EO in the EO outlet, having one or more inlets locatedabove the elevated temperature FA inlet for one or more external processstreams at lower temperature with respect to the elevated temperatureFA.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art EO/EG process and apparatus.

FIGS. 2 to 9 illustrate the apparatus and process of the EO StripperConcentrator of the invention.

FIGS. 10 to 11 illustrate the apparatus and process of the EO Stripperimpurity removal of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Herein ‘EO Stripper’ and ‘EO Stripper Concentrator’ are usedinterchangeably when describing the adapted EO Stripper of the presentinvention.

In a particular advantage the one or more external process streamscauses an increase in EO concentration and a decrease in waterconcentration in the overhead outlet of the EO Stripper Concentrator.The one or more external process streams condense water going up the EOStripper Concentrator but the EO remains gaseous. This reduces reboilerduty.

A reflux by definition is carried out with introduction of (partly)condensed top product at the top of a column, the present inventiontherefore provides a Concentrator which differs from the prior art andfrom known refluxes by introducing an external process stream at the topof the EO Stripper Concentrator.

Reference herein to an external process stream is to a stream that isderived externally from a separate process unit in communication withthe EO Stripper, and/or that is not a reflux stream, in particular isnot a reflux stream from the EO Stripper or derived from the EO Stripperoverhead, but more particularly is a concentrator stream for the EOStripper tops internal. Preferably an external process stream is derivedexternally from a separate process unit directly without cooling, orindirectly but with only partial cooling. This has the particularadvantage that the energy saving of the invention is not mitigated byenergy used in cooling the concentrator stream.

Preferably the inlet for elevated temperature FA is located in the upperpart of the EO Stripper and the inlet(s) for the one or more externalprocess streams is located in the upper part of the EO Stripper abovethe inlet for introducing elevated temperature FA.

Accordingly in the present invention, for reduction of water content inthe top, a rectifying section in the EO Stripper is not achieved with areflux of top product, but is achieved using an external process streamas hereinbefore defined.

Preferably the apparatus is an apparatus for recovery of EO andcomprises an EO Absorber which supplies the elevated temperature FAinlet of the EO Stripper Concentrator as hereinbefore defined, said EOAbsorber having an inlet for an EO gaseous stream and an inlet for LAand an outlet for FA for heating and supply to the EO StripperConcentrator. LA and FA are selected respectively from any aqueousabsorbent for absorbing EO from a gaseous stream, or containing EO.Preferably LA and FA are respectively EO-lean and EO-fat aqueousabsorbent. Absorbent is usually water optionally with any additives andentrained or accumulated process components.

Suitably stripping gas is any gas which is suitable for stripping EOfrom FA as hereinbefore defined, and is preferably selected from steamand the like.

Preferably elevated temperature FA supplied to an inlet is at atemperature in the range of from 60° C. to 150° C., preferably from 100°C. to 140° C. and the temperature of an external process stream suppliedto an inlet as hereinbefore defined is in the range of from 10° C. to80° C., preferably from 15° C. to 60° C. Preferably an external processstream is at a temperature in excess of the boiling point of EO.

Preferably the apparatus of the invention comprises inlets for supplyingone or more external process streams to the EO Stripper in a ratio of 1to 50 wt % external process stream expressed as a percentage of totalexternal process streams, preferably with respect to elevatedtemperature FA, to 50 to 99 wt % elevated temperature FA, preferably inthe range 5 wt % to 35 wt % external process streams to 65 wt % to 95 wt% elevated temperature FA.

An external process stream is suitably selected from an aqueous orgaseous stream, preferably an FA stream, a water stream, an EO streamand the like, and combinations thereof. An FA stream is suitably anyavailable FA stream which is at a temperature lower than that of theelevated temperature FA. A water stream may be any available waterstream, and may be make-up water balance or may be compensated elsewhereto restore the water balance in or related to the EO StripperConcentrator.

An external process stream comprising water may make up part of thewater balance in place of stripping gas, usually in the form of steam,or condensate which is normally added in the bottom of the EO Stripper.By adding water as external process stream as hereinbefore defined, inthe top of the EO Stripper Concentrator, the same effect on the waterbalance may be achieved.

An external process stream comprising EO may comprise EO from elsewherein the unit or from storage. Other external process streams may beenvisaged using available feeds.

One or more external process stream inlets comprising FA inlets may besupplied from an outlet for FA from an EO Absorber for forming FA bycontacting EO containing-gas and vapors with aqueous liquid phase LA,from an outlet for FA from an RA for forming FA by contacting residualEO-containing LE with aqueous liquid phase LA, or a combination thereof.

In the case that external process stream inlets comprising FA inlets aresupplied from both sources, one or more combined inlets for externalprocess stream FA may be supplied from the EO Absorber and the RA or oneor more separate external process stream FA inlets may be supplied fromthe EO Absorber and the RA respectively.

The one or more external process streams comprising FA recovered fromthe EO Absorber usually passes via a LA/FA heat exchanger with hot LA onthe other side supplied from an outlet in the bottom of the EO Stripperand supplying an inlet in the EO Absorber. The apparatus may comprise anRA in communication with the EO Absorber and EO Stripper Concentratorhaving an inlet for LA from the EO Stripper and an inlet for recoveredlight ends (LE) for conducting a further, residual, absorption of LE,and having outlets for FA and purified LE for recycle. Alternatively oradditionally therefore, the one or more external process streams maycomprise FA recovered from the RA which usually passes via a LA/FA heatexchanger with hot LA on the other side supplied from an outlet in thebottom of the EO Stripper and supplying an inlet in the RA.

The one or more external process stream inlets comprising FA inlets maybe supplied from one of the RA or EO Absorber FA outlets, or acombination thereof, as a slip stream from the FA outlets, whichbypasses or partially bypasses the LA/FA heat exchanger. The heatexchanger may accordingly be reduced, remain substantially the same sizeor may be increased in surface area.

In a particular advantage of the invention, an external FA stream mustanyway be heated for stripping, and this is usually in the LA/FA heatexchanger. There is an energy saving by adding FA in the EO Stripperabove the elevated temperature FA inlet, whereby the external processstream FA exchanges heat with the stripper contents, therebyconcentrating the overhead.

In a further advantage by condensing part of the water in the top of theEO Stripper against FA, extra heat energy integration can be obtainedthat will be able to reduce the total steam consumption for anintegrated EO/EG process.

In this case the apparatus and process of the invention provides for anenergy gain due to condensing of the water in the top of the EOStripper, thus heating up the cold FA which results in a lower energyrequirement of the EO Stripper reboiler. A small energy loss in the EOStripper due to less efficient recovery of energy in the LA/FA heatexchanger may be compensated by a small energy gain due to the highertemperature of the FA passing through the LA/FA heat exchanger,depending on the size of the heat exchanger.

In a particular advantage of the introduction of external process streamFA from the RA, the FA from the RA bottom is useful to absorb EO vapourin the EO Stripper top internal thereby reducing the total LAcirculation. For example the RA circulates 20% FA and this can lead to areduction of 5% total LA circulation. This further reduces energyconsumption.

The RA may be supplied by a combined conduit for EO containing-LE fromthe Stripper and residual EO containing-LE from an overhead gas outletfrom a LE Column which proceeds via in sequence a chiller, a cooler, avent from a LE Surge Drum which condenses out EO and water and a furtherchiller; or may be supplied directly by residual EO containing-LE fromthe overhead gas outlet from the LE Column, bypassing the chiller,cooler, LE Surge Drum and further chiller; or a combination thereof. Inthe direct supply, the EO containing LE is supplied without condensingout EO and water. This represents a unit optimisation and may representa change in overall energy consumption.

The apparatus of the invention may further comprise an inlet in the RA,suitably in the bottom part thereof, for external process stream FA. Theexternal process stream FA is supplied from the EO Absorber, to absorbEO in the RA. FA still has some capacity to absorb EO from very EO-richstreams, whilst LA is required to absorb EO from EO-poor streams. Hencethis adaptation represents a beneficial use of the absorbent available.

The apparatus of the invention may be operated at a desired pressurewhereby variations in the above features may provide additionaladvantages. In particular, a chiller may be introduced for LE in thevent conduit from the LE Surge Drum to the RA inlet for residualEO-containing LE whereby pressure may be decreased or RA decreased insize, or vice versa.

In a further optimisation the RA is supplied directly by residual EOcontaining-LE from the overhead gas outlet from a LE Column, optionallyvia a condenser, and the surge drum and accumulator may be omitted inthe overhead feed from the EO Stripper Concentrator to the LE Column.

In the apparatus of the invention, preferably in optimised form ashereinbefore defined, the RA may be located directly above the EOstripper as a separate unit or within a common shell forming a singlecolumn concentrator as a combined unit. Optionally additionally the LEColumn may be incorporated within the combined EO Stripper and RA lineup or shell, or it may be omitted.

Preferably the shell comprises an “overhead” between the EO Stripperportion and the RA portion to remove EO. This ensures that the EO doesnot all go into the RA. In this embodiment the EO overhead can gostraight to the LE column, and LE overhead is fed to the RA.

Preferably an internal condenser, such as a cold water condenser, isprovided in the top of the EO Stripper Concentrator which generates areflux and further concentrates the overhead. In this case the LE Columnmay be omitted depending on the intended use of the product stream.

The RA may be decreased in size, due to the increase in EO concentrationin the overhead and decrease in EO concentration in the LA.

In a further optimisation the RA may even be removed. In a particularadvantage of the invention the improved line up has the consequence thatby removing the RA there are no redundant streams and there is no needto divert streams. Again the LE Column may be omitted depending on theintended use of the product stream.

The RA and EO Stripper combined in a common shell may be in opencommunication or may comprise an internal division whereby each may beoperated as a separate unit with independent operating conditions suchas pressure and the like.

Combinations of the foregoing apparatus features and line ups may beenvisaged by those skilled in the art.

In a further aspect of the invention there is provided a process forimpurity removal in a process for the recovery of ethylene oxide (EO)from fat absorbent (FA) in an EO Stripper which comprises providing anelevated temperature FA feed, providing a stripping gas feed andcontacting with the FA feed at elevated temperature in the EO Stripper,obtaining an overhead EO stream and a bottoms lean absorbent (LA)stream, and removing impurities through one or more side draws from theEO Stripper. The present invention also provides an apparatus forimpurity removal in a process for recovery of EO from FA, comprising anEO stripper having an inlet for elevated temperature FA, an inlet forstripping gas for contacting at elevated temperature with the elevatedtemperature FA, an overhead outlet for EO and a bottoms outlet for LA,characterised in that the EO Stripper comprises one or more impurityremoval stages in the form of one or more side draws from the EOStripper intermediate the overhead and the bottom outlets for removingimpurities.

Preferably the apparatus for impurity removal is an apparatus forrecovery of EO from an EO-containing gas as hereinbefore described.

Suitably the apparatus removes hydrocarbon and chlorinated hydrocarbonimpurities such as aldehydes, alcohols, acids, acetals, cyclic acetals,ethers, cyclic ethers, and esters, for example formaldehyde,1,4-di-oxane, 1,4,7-tri-oxane, 1,3-di-oxolane, 2-methyl-1,3-di-oxolane,2-chloro-methyl-1,3-di-oxolane, 2-chloro-ethanol, glyoxal, oxalic acid,glycolic acid, glyoxilic acid, lactic acid, acetic acid, formic acid,and their esters.

Preferably the side draw leads to a side stripper having a strippedgaseous phase outlet for purified gases, or leads to a converter forconverting out EO and/or impurities, or to a bleed, or a combinationthereof.

A side stripper or converter may comprise an outlet for a waste waterstream or for an impurities-enriched stream.

A waste water stream or impurities-enriched stream may be separated fromthe side stripper as a bottom waste water stream or as a sideimpurities-enriched stream above a purified bottom water stream.

A side draw-off may be from any one or more locations in the EO Stripperand may be from the gas or liquid phase or a combination thereof;preferably it is from the liquid phase or combined gas and liquidphases. Preferably a side draw comprises a plurality of draw-off pointsat different levels or heights within the EO Stripper. This providesincreased stability to fluctuations in EO concentration and impurityconcentrations in the overhead and bottom and prevents build up ofimpurities. Moreover this provides for draw-off of different impurities.

Preferably an impurity-enriched stream is so concentrated in impuritythat there is no waste water, and the enriched stream may therefore bediscarded or reused within the system, for example as ballast or as partof the water balance.

Alternatively the side draw or impurity-enriched stream leads to aconverter which converts EO or impurities to a product suitable for useor for discard, eg conversion of EO to MEG, esters to non-corrosiveform, or the like.

Preferably the apparatus of the invention is for removing impuritieswhich have a relative volatility between that of EO and water. In aparticular advantage we have found that some impurities such aschlorinated cyclic acetals have a boiling point greater than both EO andwater, for example of 200° C., whereby they might be expected to residein a waste water stream, but that they have a relative volatilitybetween that of EO and water, whereby they may surprisingly be separatedfrom the bottom and top streams by the side draw of the invention.

Accordingly the apparatus for impurity removal is operated according toa single specification that the overhead comprises substantially noimpurity, and that impurity builds up in the EO Stripper. Preferably theapparatus provides an overhead EO concentration of greater than or equalto 80 wt %, more preferably 88 wt %, more preferably 95 wt %, mostpreferably greater than or equal to 98 wt %, especially greater than orequal to 99 wt % or 99.5 wt %. Thereby the overhead is substantiallyfree of some or most impurities.

Preferably the apparatus for impurity removal comprises means forconcentrating the overhead from the EO Stripper. Thereby in a particularadvantage substantially all impurities are concentrated within the EOStripper and do not leave via the overhead, whereby substantially pureoverhead is obtained. The EO Stripper may comprise a reflux in the topof the EO Stripper or in the overhead. This concentrates the overhead,for example gives approximately 80 wt % EO or more preferably 88 wt % EOin the overhead.

Alternatively or additionally an apparatus for impurity removal ispresent in an EO Stripper Concentrator of the first aspect of theinvention comprising means for concentrating the overhead ashereinbefore described. In a particular advantage in the apparatuscomprising a liquid side draw any residual impurities above the sidedraw are condensed within the EO Stripper Concentrator as hereinbeforedefined by means of the external process stream inlets as hereinbeforedefined. Thereby the overhead is further concentrated, and for examplecomprises approximately 90 wt % EO. More preferably the apparatus forimpurity removal is present in an EO Stripper Concentrator comprisingadditionally a reflux in the top of the EO Stripper Concentrator or inthe overhead. Thereby the overhead is further concentrated, and forexample comprises approximately 99 wt % or more EO. We have found thatthis impurity removal has excellent effect due to highly concentratedoverhead.

In a particular advantage of the further embodiment of the inventioncomprising a side stripper to the EO Stripper, the removal of impuritiesreduces downstream problems such as corrosion, product quality, wastegeneration and the like.

Preferably an apparatus of the present invention is part of an EO/EGunit for the conversion of ethylene to EO, and thereafter to EG, orpurified to high purity EO, comprising an EO Absorber having an inletfor reaction gas and an inlet for Absorbent, and an outlet for FAcomprising EO, and comprising an EO Stripper having an inlet forelevated temperature FA and outlets for stripped LA and for EO, theapparatus comprising additionally one or more inlets in an EO StripperConcentrator for external process streams for concentrating the EOoutlet stream, and/or comprising one or more impurity removal stages inthe form of one or more side draws from the EO Stripper or EO StripperConcentrator as hereinbefore defined.

As hereinbefore described in one aspect of the invention there isprovided a process for recovery of EO from FA comprising providing afeed of elevated temperature FA to an EO Stripper, providing a strippinggas feed and contacting at elevated temperature with the elevatedtemperature FA feed, and obtaining stripped LA and an EO containing gas,characterised by providing one or more external process stream feeds tothe EO Stripper at a location above the elevated temperature FA feedthereby providing an EO Stripper Concentrator for concentrating EO inthe EO containing gas, and at a lower temperature with respect to theelevated temperature FA feed.

The process of the invention gives a purified EO product stream from theoverhead of the EO Stripper Concentrator which is more concentrated inEO and less concentrated in water vapour and impurities than thecorresponding process without external process stream feed. The one ormore external process stream feeds condense water going up the EOStripper but the EO remains gaseous.

Preferably the water content in the EO stripper overhead stream in theprocess of the invention is in the range from pure EO to 30 wt % water.Preferably the process provides an EO Stripper overhead streamcomprising higher EO concentration, in comparison to the prior artprocess. This leads to savings on stripper duty and low pressure steamsavings.

The present invention is a novel way to reduce the water content in theEO Stripper tops, by for example using FA feed partially bypassing theFA feed bottoms exchanger or by using external process stream feeds ashereinbefore defined from elsewhere. By having an external processstream feed at a lower temperature than the FA feed, in the top of theStripper the water in the top is condensed with the external processstream FA stream, thus reducing the duty of the reboiler and providing amore energy efficient process. Other process modifications also becomepossible leading to a simpler operation and lower energy demands.

The process of the invention is characterised by further advantagescorresponding to those as hereinbefore stated for the hereinbeforedefined apparatus.

Preferably the process comprises providing the feed of elevatedtemperature FA in a stripped vapors zone in the upper part of the EOStripper Concentrator, and providing the one or more feeds of one ormore external process streams in the upper part of the EO StripperConcentrator, above the feed for elevated temperature FA.

Preferably the process is a process for recovery of EO and comprisesabsorbing EO with LA and obtaining FA for heating to elevatedtemperature and supply of elevated temperature FA feed to the EOStripper Concentrator as hereinbefore defined.

Preferably an elevated temperature FA feed as hereinbefore defined is ata temperature in the range of from 60° C. to 150° C., preferably from100° C. to 140° C., and the temperature of an external process stream isin the range of from 10° C. to 80° C., preferably from 15° C. to 60° C.Preferably the external process stream is at a temperature in excess ofthe boiling point of EO.

The process may comprise providing one or more external process streamfeeds to the EO Stripper in a ratio of 1 to 50 wt % external processstream expressed as a percentage of total external process streams,preferably with respect to elevated temperature FA, to 50 to 99 wt %elevated temperature FA, preferably in the range 5 wt % to 35 wt %external process streams to 65 wt % to 95 wt % elevated temperature FA.Whilst there is no limitation as such on the amount of external processstream FA to introduce, and the input to the EO Stripper might compriseup to 100% external process stream FA, without the need to introduceadditional steam, particularly significant concentration effect isobtained with external process streams in proportions as hereinbeforedescribed.

Preferred external process stream feeds are as hereinbefore described.By selecting the nature of external process stream feed, theconcentration of EO in the EO Stripper overhead may be influenced toadvantage.

The one or more external process stream feeds comprising FA may compriseFA from an EO Absorber for forming FA by contacting EO containing-gasand vapors with aqueous liquid phase LA, or may comprise FA from an RAfor forming FA by contacting residual EO-containing LE with LA, or acombination thereof.

In the case that external process stream feeds comprise FA from bothsources, one or more combined feeds for external process stream FA feedmay be supplied from the EO Absorber and the RA or one or more separateexternal process stream FA feeds may be supplied from the EO Absorberand the RA respectively.

The one or more external process stream feeds comprising FA feed fromthe EO Absorber usually passes via a LA/FA heat exchanger with hot LA onthe other side supplied from the bottom of the EO Stripper as feed tothe EO Absorber. The process may comprise providing an LA feed from theEO Stripper to a RA, in communication with the EO Absorber and EOStripper Concentrator, and contacting with a recovered LE feed forconducting a further, residual, absorption of LE, and obtaining FA andpurified LE for recycle. Alternatively or additionally therefore, theone or more external process stream feeds may comprise FA recovered fromthe RA which usually passes via a LA/FA heat exchanger with hot LA onthe other side obtained from the bottom of the EO Stripper as feed forthe RA.

The one or more external process stream feeds comprising FA may beobtained from one of the RA or EO Absorber, or a combination thereof, asa slip stream from the FA streams, which bypasses or partially bypassesthe LA/FA heat exchanger. The heat exchange duty may accordingly bereduced, remain substantially the same or may be increased.

The process may comprise supplying the RA from a combined EOcontaining-LE feed from the Stripper and residual EO containing-LE feedfrom the overhead from a LE Column via in sequence a chiller stage, acooler stage, venting from a LE Surge Drum which condenses out EO andwater and a further chiller stage; or supplying directly residual EOcontaining-LE feed from the overhead from the LE Column, bypassing thechiller stage, cooler stage, condensation and further chiller stage; ora combination thereof. In the direct supply process, EO containing-LEfeed is supplied without condensing out EO and water. This represents aprocess optimisation and may represent a change in overall energyconsumption.

The process may further comprise supplying external process stream FA inthe RA, preferably in the bottom part thereof. The external processstream FA is supplied from the EO Absorber to absorb EO in the RA.

The process of the invention may be operated at a desired pressure,preferably from above atmospheric pressure up to 4 bar (400 kPa),whereby variations in the above features may provide additionaladvantages. In particular, a chilling stage may be introduced forresidual EO-containing LE vented from the LE Surge Drum and supplying tothe RA whereby pressure may be decreased or RA volumes decreased, orvice versa.

In a further embodiment the process comprises supplying the RA directlywith residual EO containing-LE from the overhead from a LE Column,optionally via a condensor stage and omitting a surge and accumulatorstage in the overhead feed from the EO Stripper Concentrator to the LEColumn.

In the process of the invention, preferably optimised as hereinbeforedescribed, the RA stage may be conducted directly above the EO StripperConcentrator stage in separate process stages or within a common shellforming a single column concentrator as a combined process stage.Optionally additionally a LE separation stage may be incorporated withinthe EO Stripper and RA stages or integral therewith.

Preferably the shell comprises an “overhead” between the EO Stripperportion and the RA portion to remove EO. This ensures that the EO doesnot all go into the RA. In this embodiment the EO overhead can godirectly as feed to the LE column, and LE overhead is feed to the RA.

Preferably a reflux, such as a cold water reflux, for example generatedby an internal condenser, is provided in the top of the EO StripperConcentrator which further concentrates the overhead. In this case theseparation stage in the LE Column may be omitted depending on theintended use of the product stream.

The RA stage may be decreased in size, due to the increase in EOconcentration in the overhead and decrease in EO concentration in theLA.

In a further optimisation the RA stage may even be removed. Again theseparation stage in the LE Column may be omitted depending on theintended use of the product stream.

The RA and EO Stripper combined in a common shell may be integral or maybe operated as separate processes with independent operating conditionssuch as pressure and the like.

Combinations of the foregoing process features may be envisaged by thoseskilled in the art.

As hereinbefore described in a further aspect of the invention there isprovided a process for impurity removal in a process for recovery of EOfrom FA in an EO Stripper comprising an elevated temperature FA feed forcontacting with stripping gas at elevated temperature, and obtaining anoverhead EO stream and a bottoms LA stream, characterised in that the EOStripper comprises one or more impurity removal stages in the form ofone or more side draws from the EO Stripper for removing impuritiesintermediate the overhead and bottoms streams.

Preferably the process for impurity removal is a process for recovery ofEO from an EO-containing gas.

Suitably the process removes hydrocarbon and chlorinated hydrocarbonimpurities such as aldehydes, alcohols, acids, acetals, cyclic acetals,ethers, cyclic ethers, and esters, for example formaldehyde,1,4-di-oxane, 1,4,7-tri-oxane, 1,3-di-oxolane, 2-methyl-1,3-di-oxolane,2-chloro-methyl-1,3-di-oxolane, 2-chloro-ethanol, glyoxal, oxalic acid,glycolic acid, glyoxilic acid, lactic acid, acetic acid, formic acid andtheir esters.

Preferably the side draw feeds a side stripper having a stripped gaseousphase outlet for purified gases, or feeds a converter for converting EOand/or impurities, or feeds a bleed, or a combination thereof.

A side stripper or converter stage may produce a waste water stream oran impurities-enriched stream. A waste water stream orimpurities-enriched stream may be separated from the side stripper as abottom waste water stream or as a side impurities-enriched stream abovea purified bottom water stream.

A side draw off may be from any one or more locations in the EO Stripperand may be from the gas or liquid phase or a combination thereof,preferably is from the liquid phase or combined gas and liquid phases.Preferably a side draw comprises a plurality of draw off points atdifferent levels or heights within the EO Stripper. This providesincreased stability to fluctuations in EO concentration and impurityconcentrations in the overhead and bottom and prevents build up ofimpurities. Moreover this provides for draw off of different impurities.

Preferably an impurity-enriched stream is so concentrated in impuritythat there is no waste water, and the process comprises discarding theenriched stream or reusing within the system, for example as ballast oras part of the water balance.

Alternatively the process comprises providing the side draw orimpurity-enriched stream to a converter and converting EO or impuritiesto a product suitable for use or for discard, eg conversion of EO toMEG, esters to non-corrosive form, or the like.

Preferably the process of the invention is for removing impurities whichhave a relative volatility between that of EO and water. In a particularadvantage we have found that some impurities such as chlorinated cyclicacetals have a boiling point greater than both EO and water, for exampleof 200° C., whereby they might be expected to reside in a waste waterstream, but that they have a relative volatility between that of EO andwater, whereby they may surprisingly be separated from the bottom andtop streams by the side draw of the invention.

Accordingly the process is operated according to a single specificationthat the overhead comprises substantially no impurity, and that impuritybuilds up in the EO Stripper. Preferably the process provides anoverhead EO concentration of greater than or equal to 80 wt %, morepreferably 88 wt %, more preferably 95 wt %, most preferably greaterthan or equal to 98 wt %, and especially preferably greater than orequal to 99 wt % or 99.5 wt %. Thereby the overhead is substantiallyfree of some or most impurities.

Preferably the process comprises providing a side draw-off in thegaseous and/or liquid phase of the EO Stripper, preferably at the pointof greatest concentration of impurities, typically the upper to middledistillation stages in the EO Stripper such as the third, fourth orfifth concentrator tray in say a 20 stage EO Stripper column. Anyimpurities leaving the EO Stripper via the bottom will lead toaccumulation of impurities in the LA/FA circuit which are then drawn offin the side draw of the EO Stripper.

Preferably the process comprises concentrating the overhead from the EOStripper. Thereby in a particular advantage substantially all impuritiesare concentrated within the EO Stripper and do not leave via theoverhead, whereby substantially pure overhead is obtained. The processmay comprise operating a reflux in the top of the EO Stripper or in theoverhead. This concentrates the overhead, for example givesapproximately 80 wt % or more preferably 88 wt % EO in the overhead.

Alternatively or additionally a process for impurity removal is presentin a EO Stripper Concentrator process of the first aspect of theinvention comprising means for concentrating the overhead ashereinbefore described. In a particular advantage in the processcomprising providing a liquid side draw any residual impurities abovethe side draw are condensed within the EO Stripper Condensor ashereinbefore defined by means of the external process stream inlets ashereinbefore defined. Thereby the overhead is further concentrated, forexample comprises approx 90 wt % EO. More preferably the process forimpurity removal is present in an EO Stripper Concentrator process ashereinbefore defined comprising additionally a reflux in the top of theEO Stripper Concentrator on in the overhead. Thereby the overhead isfurther concentrated, for example comprises approx 99 wt % or more EO.We have found that this impurity removal has excellent effect due tohighly concentrated overhead.

In a further advantage the external process stream concentrator processof the invention causes condensation of heavy contaminants above theflasher of the EO Stripper and avoids contaminants leaving in the EOStripper overhead. In particular this is useful for heavy contaminantssuch as chlorinated hydrocarbons, including alcohols, organic acids,aldehydes, acetals and esters.

Preferably a process of the invention is part of an EO/EG process forthe conversion of ethylene to EO with formation of byproducts, water andCO₂, and thereafter converting to EG, or purifying to high purity EO,comprising recovering EO by introducing into an EO absorber andcontacting with absorbent to form FA and introducing elevatedtemperature FA into an EO stripper to separate absorbent from productEO, the process comprising additionally introducing one or more externalprocess stream feeds into the EO Stripper Concentrator by the process ashereinbefore described and/or comprising one or more impurity removalstages in the form of one or more side draws to the EO Stripper or EOStripper Concentrator as hereinbefore defined.

The invention is now illustrated in non-limiting manner with respect tothe following Examples and Figures.

In FIG. 1 the overhead product (14) of the EO Stripper (4) is partlycondensed against chiller and/or coolers (7) and sent via line (19) tothe LE Column (6) for removal of light components. The overhead vapour(20) of the LE Column is sent back to the LE Column Surge Drum (8). Thelight components gas stream is vented from the LE Column Surge Drum,passes through the RA (2) via line 22 to recover EO and is sent back tothe recycle gas (23) by means of the Residual Gas Compressor (notshown).

The RA (2) is operated with cold LA (18) as scrubbing medium and thebottom stream (12) is combined with the FA (11) from the EO Absorber (1)and sent back to the EO Stripper (4) via line 13 for recovery of the EO.

The bottom stream (24) of the LE Column (6), essentially a water/EOmixture, is fed either to an EO Purification Column (9) for recovery ofhigh purity EO and/or fed directly to a Glycol Reactor (not shown).

In the prior art process of FIG. 1 if the pressure in the EO Stripper(4) is lowered, an optional chiller (10) may be present in the LE gasstream (21) from the LE column Surge Drum (8).

In FIG. 2 the FA (11) from the bottom of the EO Absorber (1) is combinedwith the bottom stream (12) of the RA (2) as in FIG. 1, and part of thismixture is introduced as external process stream feed (25) to the EOStripper Concentrator (4), above the elevated temperature FA feed (13)and at a lower temperature thereto.

Alternatively or additionally optional external process stream feed(s)(26) to the EO Stripper Concentrator (4) is/are from another externalsource. Such external process stream (26) may optionally also be presentin the apparatus and method illustrated in the subsequent FIGS. 3 to 11(there not shown).

In FIG. 3 there is no combination of FA from the bottom (11) of the EOAbsorber (1) with the bottom stream (12) of the RA (2) as in FIG. 2,rather they are fed separately (25, 27) to the EO Stripper. Part of thecold FA (11) from the EO Absorber and the bottom stream (12) of the RA(2) are used as external process stream feed (25, 27) to the EO StripperConcentrator (4) to get the same effect as in FIG. 2.

In FIG. 4 the overhead gas (20) from the LE Column (6) is no longercondensed against cooling water and a chiller as in FIGS. 1 to 3, butinstead is absorbed (28) in the RA (2).

In FIG. 5 the RA (2) line up is optimised: a small portion of the coldFA stream (11) of FIGS. 1 to 4 is used (29) to absorb EO in the bottompart of the RA (2), whereas LA (18) is used in the top part.

FIG. 6 shows the system of FIG. 4 wherein the function of theaccumulator between the EO Stripper condensors (7) and the LE Column (6)in the original outlet is redundant, and these units can be removed. Anoptional chiller (30) may be included in the overhead (20) from the LEColumn (6) to the inlet (22) to the RA (2).

FIGS. 7 and 8 show the same functional system of FIG. 6 but with the RA(2) located on top of the EO Stripper (4) or integrated with the EOStripper (4) into one shell (31). The integrated single shell (31) mayhave different or same diameters. In the combined shell configuration(31) shown in FIG. 8 the LE Column may be omitted.

FIG. 8 shows the system of FIGS. 2 to 9 with integrated shell (31) andmeans for condensing the EO Stripper overhead by reflux (32) to give anoverhead stream (14) of greater than or equal to 99 wt % EO. This lineup provides for very high concentration EO in the EO Stripper overheadsuch that the overhead can go direct to EO purification and the LEColumn is dispensed with. The residual LE, eg CO₂, is acceptable infeedstock to downstream processes such as an EG process. If LE removalis desired a stripper in the overhead (not shown) may be included.

FIG. 9 shows the system of FIG. 8 with the RA completely removed. An LEcolumn may be present if desired depending on the intended use of theproduct stream (14).

FIG. 10 shows the side draw (33) for impurity removal with means forcondensing in the form of an overhead reflux (32) of FIGS. 8 and 9 andoptionally additionally with the external process stream concentrator(25, 27) of FIGS. 2 to 8.

FIG. 11 shows the system of FIG. 10 leading to a side stripper (34) withreturn of purified EO (35) to the EO Stripper (4), and removal ofimpurities in a waste water stream or a concentrated impurity stream(36). In this line up, for example, the EO Stripper (4) may comprise 20theoretical stages, with the elevated temperature FA feed (13) enteringthe column preferably at stages 6 to 9, e.g. stage 9, any lowertemperature FA feed (25) entering above preferably at stages 5 to 7,e.g. stage 6, and with the side draw-off preferably at stages 3 to 5,e.g. at stage 4, to the side stripper (34) having some 5 theoreticalstages. As an alternative to theoretical stages, or plates provided bypacking, one or both stripper columns may operate with physical trays.

EXAMPLE 1

In the system of FIG. 2 with 20% bypass of FA we get 5.8% H₂O in EOstripper overhead.

Energy necessary to evaporate EO  4941 kW Energy necessary to heat up FAin column 30159 kW Energy necessary to evaporate water 11293 kWFor bypass of 0%-20% cold FA the following results are obtained:

TABLE 1 % bypass 0 5 10 15 20 Reduction water over top 0 −4054 −8108−12162 −16216 [kW] Energy loss due to bypass 0 4369 8739 13108 17477 inLA/FA heat exchanger (3) [kW] Energy gain due to higher 0 −1780 −3379−4779 −5997 hot FA temperature [kW] Reduction of energy 0 −296 −591 −887−1183 content EO Concentrator tops [kW] Overall duty reduction 0 −1761−3334 −4720 −5919 [kW]Optimum bypass is estimated at 25%-30% giving a heating duty reductionof approx 10 MW.

EXAMPLE 2

For the apparatus and methods of FIGS. 1 and 11, Table 2 shows impuritylevels in the EO Stripper/Concentrator top, and the associated energyperformance.

FIG. 1 FIG. 11 Heat duty EO Stripper/Concentrator/ 64.5 58.5 Mwatt Dutyside stripper (34)/Mwatt 0.5 Feed temperature FA1 (13)/° C. 104.5 111.2Feed temperature FA2 (25)/° C. 37 FA1 t/h (13) 1911.2 1624.5 FA2 t/h(25) 286.7 Temp EO Stripper/Concentrator Top 99.7 26.0 (14)/° C. Temp EOStripper/Concentrator Bottom 119.4 120.9 (16)/° C. EO purity OVHD EO64.50 99.60 Stripper/Concentrator (14)/% Impurity top EO 17.0 0.89Stripper/Concentrator (14)/ppm

From the Table it is clear that impurity removal may be operated withthe FA bypass of Example 1 and still gain an energy reduction comparedto the conventional operation with no impurity removal. Impurity removalresults in a reduction from 17 ppm to 0.89 ppm impurity in the EOStripper/Concentrator top.

1. A process for impurity removal in a process for the recovery ofethylene oxide (EO) from fat absorbent (FA) in an EO Strippercomprising: providing an elevated temperature FA feed, providing astripping gas feed and contacting with the FA feed with the strippinggas feed at elevated temperature in the EO Stripper, obtaining anoverhead EO stream and a bottoms lean absorbent (LA) stream, andremoving impurities through one or more side draws from the EO Stripper.2. The process of claim 1, wherein the impurities have a relativevolatility between that of EO and water.
 3. The process of claim 2,wherein hydrocarbon and chlorinated hydrocarbon impurities are removed.4. The process of claim 2, wherein a side draw feeds a side stripperhaving a stripped gaseous phase outlet for purified gases.
 5. Theprocess of claim 2, wherein a side draw feeds a converter for convertingEO and/or impurities.
 6. The process of claim 5, wherein the converterproduces a waste water stream or an impurities-enriched stream.
 7. Theprocess of claim 4, wherein the side stripper produces a waste waterstream or an impurities-enriched stream.
 8. The process of claim 1,further comprising operating a reflux in the top of the EO Stripper. 9.The process of claim 1, further comprising using EO from the EO streamto make ethylene glycols (EG).